The present invention relates generally to railway fluid pressure brake systems. More particularly, the invention concerns an emergency brake control valve and a system incorporating the same that enables the locomotive engineer to remotely initiate emergency braking at the rear of the train.
In a typical railway train braking system, each vehicle is fitted with a brake pipe, which extends along the length of the vehicle and is coupled to the vehicle's brake cylinders through service and emergency reservoirs and various valves. At each end of the vehicle, the brake pipe is coupled to a "glad-hand" connector through an angle cock and a flexible hose. During assembly of a train, the glad-hand connectors of adjacent vehicles are interconnected to form a continuous brake pipe extending from the locomotive of the train to the last vehicle thereof. The locomotive includes a source of air pressure that is coupled to the locomotive's brake pipe by various valves, including service and emergency control valves accessible to the locomotive engineer.
When the brake pipe interconnections have been made, the angle cock at the far end of the last vehicle is closed and the remaining angle cocks are open to accordingly form a continuous, closed brake pipe extending from the locomotive to the last vehicle. Through the valves of the locomotive, the brake pipe is charged from the source of air pressure to a predetermined pressure value, (e.g., 85 psi). This predetermined brake air pressure causes the pistons in the brake cylinders at each vehicle to be withdrawn to effect a full brake release, and pressurizes the various reservoirs.
When application of either the service brakes or the emergency brakes is desired, the appropriate control valve in the locomotive is actuated by the engineer so as to result in a reduction in brake pipe air pressure at the locomotive, which, thereafter, rapidly propagates along the brake pipe. At each vehicle, the valves sense the differential between the reservoir air pressure and the brake pipe air pressure and apply the brakes in response thereto. For the service brakes, the brakes are applied in proportion to the magnitude of the pressure differential. In order to release the brakes after a brake application, the engineer actuates one of the valves to cause the brake pipe air pressure to be restored to the full release value if a full brake release is desired or to an intermediate value if a partial brake release is desired.
In emergency situations, actuation of the emergency control valve in the locomotive produces a pulse of air that travels from the locomotive rearwardly along the brake pipe. At each vehicle, the valves that control emergency braking sense this pulse and, in response thereto, exhaust air from the brake pipe. This results in full application of the brakes. The braking application mirrors the propagating control pulse, so that emergency braking occurs first at the front of the train and thereafter propagates rearwardly through each vehicle.
Railway braking systems also typically include manually operated valves that are accessible to persons on the rear of a train and that can be actuated to apply the brakes from the rear. These mechanical valves are often employed to manually apply the brakes when the train is backing up. Since such manually operated valves are also typically present on each car of the train, braking can also be manually initiated at each car. While these valves can be used to initiate emergency braking beginning at some point other than the locomotive, they are not usually so employed since operators are not often present on the intermediate cars of the train or on the last car of a cabooseless train. Accordingly, front-of-train initiation of braking remains the sole practical means for effecting emergency braking in known systems.
In most situations, initiating emergency braking at the front of the train is a safe and effective way to fully apply the brakes. A serious and potentially dangerous situation occurs, however, where dirt or debris creates a blockage at some point along the brake pipe. If the blockage is substantial enough to prevent transmission of the propagating control pulse, emergency braking will not occur at those vehicles located rearwardly of the blockage.
From the foregoing, it can be appreciated that it would be extremely useful for the engineer to be able to initiate emergency braking at an intermediate car or the rear of the train in those situations in which an accumulation of dirt or debris in the brake pipe renders the normal front-of-train initiation of emergency braking ineffective. In other emergency braking situations, such as those involving lengthy trains, it would also be desirable to provide the engineer with a choice between initiating emergency braking at the front, rear, or an intermediate position of the train or simultaneously at more than one point. Heretofore, no means have been developed by which such rear-of-train or intermediate car emergency braking may be initiated.